M2M (Machine-to-Machine, machine-to-machine) communication refers to a generic term for a series of technologies and technology combinations that apply various communications network and information sensing and processing to implement data communication and interaction between a machine and a machine, and between a machine and a human. A communication scenario of an M2M device is small data transmission defined by 3GPP. Small data indicates that a terminal UE (User Equipment, user equipment) only sends/receives a small amount of data.
In the prior art, a small data transmission method is defined. Specifically, small data in an uplink direction or a downlink direction is transported by using a generic NAS transport message between a UE and a serving node, a T5 interface between the serving node and an MTC gateway MTC-IWF (machine type communication interworking function) device, and a Tsp interface between the MTC-IWF device and a server. In the solution, specific steps for transmitting downlink small data are as follows:
1: The server sends, to the MTC-IWF device through the Tsp interface, a message carrying the small data in the downlink direction.
2: After receiving the message sent by the server, the MTC-IWF device queries an HLR (Home Location Register, home location register)/HSS (Home Subscriber Server, home subscriber server) storing UE subscription data and acquires information of the serving node serving the UE.
3: The MTC-IWF device sends, to the serving node through the T5 interface between the MTC-IWF device and the serving node, the message carrying the small data.
4: The serving node sends a DOWNLINK_GENERIC_NAS_TRANSPORT message to the UE, where the message carries small data that needs to be sent to the UE.
It can be known from the foregoing method for transmitting small data that, in the prior art, each time an MTC-IWF device sends small data to a UE, the MTC-IWF device needs to query an HLR/HSS to obtain routing information of the UE. This brings, if frequency of sending the small data is relatively high, great signaling load to the HLR/HSS in a scenario in which downlink data is sent frequently. In addition, if multiple such applications run on the UE simultaneously, multiple servers send small data to the UE continuously and frequently. If a lot of UEs are installed with and use such applications, in the process of sending the small data in the foregoing solution, signaling load caused by querying the HLR/HSS further increases, and therefore network congestion may be caused.